A former police informant who spied on protest groups is planning to sue police for the consequences of his decade of deception.

Rob Gilchrist was outed in December 2008 after his girlfriend, animal rights and Labour activist Rochelle Rees, stumbled across police emails when he asked her to fix his computer.

Gilchrist, now in his mid-40s, was a member of many of the groups on which he reported to police. He has since suffered from depression and says his life has been threatened.

"He says, ‘Because of all this I have become mentally ill'," his lawyer Tony Ellis said in the High Court at Wellington.

Gilchrist spent about 10 years spying on Greenpeace, anti-Iraq war groups, and poverty and beneficiary rights groups, among others.

In 2008 he told the Sunday Star-Times that he did not think the people in those groups were security threats, and he got stuck in something he was not proud of but found it hard to get out.

It was alleged at the time that police were paying him $600 a week, plus expenses.

His intended claim against police was before the court last week. Ellis asked police to divulge some of the information they held about Gilchrist.

The claim includes the allegation that Gilchrist was used as a "walking search warrant", so police avoided having to ask the proper authorities, such as judges, to issue warrants.

In a draft claim for more than $500,000 and declarations against police, it is alleged that police might have deliberately leaked Gilchrist's identity, or that not enough was done to avoid him being identified.

It is understood the claim seeks $300,000 for lost income, $100,000 for factors such as distress and humiliation, $150,000 in aggravated damages, plus extra amounts to cover medical expenses, relocation, re-establishment and retraining costs.

Ellis told Justice Jill Mallon a claim had been drafted but he wanted information from police to firm up details, including the exact period Gilchrist worked for police, and how much he was paid.

The claim was not made rashly and he wanted to be sure of his ground before filing it, he said. It was not an attempt to embarrass police.

The Crown said the intended claim involved allegations only. Whether there was any truth to them was "another matter".

Its lawyer, Sarah McKenzie, said the proper time to ask for the details was after the claim was filed. Because of the sensitivity of the police informant programme, a "very senior" police officer would personally have to gather information relating to Gilchrist.

The "vast tract of information" being sought was not necessary to launch the proceeding, Ms McKenzie said. Parts of it might never have to be supplied because, as a matter of law, some of Gilchrist's case could not succeed.

For instance, he could not sue for the breach of other people's rights, she said. Some of the information was already known to Gilchrist, and other parts of the request lacked specificity.

Justice Mallon reserved her decision on the information request.

In March 2008, Gilchrist allegedly told police about a Greenpeace plan to attempt to stop a coal ship leaving Lyttelton. Police intervened and six people were arrested as Gilchrist filmed the scene from the shore. In August 2006 he went to Auckland on behalf of police to collect up-to-date photographs of activists.

It was reported in 2008 that the main groups he monitored were Save Happy Valley, which opposed coal mining, Auckland Animal Action, and Peace Action Wellington. He also forwarded emails from the Green Party and Workers Party to police.

When he was among the activist groups, he was said to be an advocate of radical, sometimes illegal, action. He was said to make a "fuss" about looking for undercover police and used a radio scanner to search for signs of police interest.

THE STORY SO FAR

Rob Gilchrist was a protester who was "turned" to spy on activist groups for police.

In early 2008 Gilchrist revealed that a security consultant working for Solid Energy had tried to employ him to pass on information about several protest groups.

Gilchrist recorded a meeting with the man in Hagley Park and afterwards phoned Sunday Star-Times.

The security consultant offered $500 a week.

Later that year his girlfriend, a fellow activist, found he was already working for the police.

Living in Christchurch he worked his dual role for nearly 10 years before his emails to and from police were discovered and he was publicly exposed in December 2008.